A switching element of the pre-cited type is disclosed in the generic prior art document DE 199 15 531 which shows a switchable cam follower for a tappet push rod drive. The high-position stop for defining the relative position is formed by a piston-like element arranged in the inner element. This piston-like element projects radially outward into a longitudinal groove of the outer element. In the axially extracted state of the inner element from the outer element, the piston-like element abuts against one end of the longitudinal groove. The purpose of this is to create an aligned arrangement of a coupling bore made in the outer element for a piston arranged in the inner element for achieving coupling.
A drawback of this prior art is that an adjustment of lash in the coupling is relatively complicated and cost-intensive. It is clear that the reception (coupling bore) in the outer element for receiving the piston must be configured with a slight lash relative to the outer peripheral surface of the piston. This lash and the high position differ from switching element to switching element due to fabrication conditions. The relatively wide range of variance of this mechanical idle travel in switching elements is, however, undesirable.
In other words, a lash, i.e. an idle travel that the inner element undergoes relative to the outer element upon coupling and loading by the cam till the outer element participates in the force flow from the cam can be compensated by an appropriate dimensioning of the cam contour. In practice, however, this results in a relatively large dispersion of lash. This leads to an undesired variance of the overlap of the intake and exhaust valves. Besides this, an undesired large amount of wear occurs if the lash between the coupling piston and its surrounding reception is too large.
To keep the coupling lash or its variance within acceptable limits, the prior art has recourse to a grouping of the coupling pistons. This procedure is extremely expensive from the point of view of fabrication and measuring techniques. For example, the switching elements are first completely mounted, the lash is then measured following which, the switching elements are dismounted again and an appropriate piston is then chosen for coupling. It is equally conceivable to group the high-position stops provided on the longitudinal grooves of the outer elements.